There are many corrosion resistant nickel-base alloys containing chromium and other elements selected to provide corrosion resistance in particular corrosive environments. These alloys also contain elements selected to provide desired mechanical properties such as tensile strength and ductility. Many of these alloys perform well in some environments and poorly in other corrosive environments. Some alloys which have excellent corrosion resistance are difficult to form or weld. Consequently, the art has continually tried to develop alloys having a combination of corrosion resistance and workability which enables the alloy to be easily formed into vessels, piping and other components that have a long service life.
British Patent No. 1,512,984 discloses a nickel-base alloy with nominally 8-25% chromium, 2.5-8% aluminum and up to 0.04% yttrium that is made by electroslag remelting an electrode that must contain more than 0.02% yttrium. U.S. Pat. No. 4,671,931 teaches the use of 4 to 6 percent aluminum in a nickel-chromium-aluminum alloy to achieve outstanding oxidation resistance by the formation of an alumina rich protective scale. Oxidation resistance is also enhanced by the addition of yttrium to the alloy. The iron content is limited to 8% maximum. The high aluminum results in the precipitation of Ni3Al gamma prime precipitates which offers good strength at high temperature, especially around 1400° F. U.S. Pat. No. 4,460,542 describes an yttrium-free nickel-base alloy containing 14-18% chromium, 1.5-8% iron, 0.005-0.2% zirconium, 4.1-6% aluminum and very little yttrium not exceeding 0.04%. with excellent oxidation resistance. An alloy within the scope of this patent has been commercialized as HAYNES® 214® alloy. This alloy contains 14-18% chromium, 4.5% aluminum, 3% iron, 0.04% carbon, 0.03% zirconium, 0.01% yttrium, 0.004% boron and the balance nickel.
Yoshitaka et al. in Japanese Patent No. 06271993 describe an iron-base alloy containing 20-60% nickel, 15-35% chromium and 2.5-6.0% aluminum which requires less than 0.15% silicon and less than 0.2% titanium.
European Patent No. 549 286 discloses a nickel-iron-chromium alloy in which there must be 0.045-0.3% yttrium. The high levels of yttrium required not only make the alloy expensive, but they can also render the alloy incapable of being manufactured in wrought form due to the formation of nickel-yttrium compounds which promote cracking during hot working operations.
U.S. Pat. No. 5,660,938 discloses an iron-base alloy with 30-49% nickel, 13-18% chromium, 1.6-3.0% aluminum and 1.5-8% of one or more elements of Groups IVa and Va. This alloy contains insufficient aluminum and chromium to assure that a protective aluminum oxide film is formed during exposure to high temperature oxidizing conditions. Further, elements from Groups IVa and Va can promote gamma-prime formation which reduces high temperature ductility. Elements such as zirconium can also promote severe hot cracking of welds during solidification.
U.S. Pat. No. 5,980,821 discloses an alloy which contains only 8-11% iron and 1.8-2.4% aluminum and requires 0.01-0.15% yttrium and 0.01-0.20% zirconium.
Unfortunately, the alloys disclosed in the aforementioned patents suffer from a number of welding and forming problems brought on by the very presence of aluminum particularly when present as 4 to 6 percent of the alloy. The precipitation of Ni3Al gamma prime phase can occur quickly in these alloys during cooling from the final annealing operation, resulting in relatively high room temperature yield strengths with corresponding low ductility even in the annealed condition. This makes bending and forming more difficult compared to solid solution strengthened nickel base alloys. The high aluminum content also contributes to strain age cracking problems during welding and post-weld heat treatment. These alloys are also prone to solidification cracking during welding, and, in fact, a modified chemistry filler metal is required to weld the commercial alloy, known as HAYNES® 214® alloy. These problems have hindered the development of welded tubular products and have restricted the market growth of this alloy.